Processes for converting hydrocarbons



destroy their efiectiveness.

Patented Nov. 16, 1937 UNITED STATES PATENT OFFICE Frederick E. Frey andWalter F. Huppke, Bartlesvillc, Okla, assignors to Phillips PetroleumCompany, Bartlesville, Okla, a corporation of Delaware No Drawing.Original application May 2, 1934,

Serial No. 723,608. Divided and this application April 15, 1935, SerialNo. 16,512

3 Claims. 01. 260-170) This appliion is a division of co-pendingapplication Serial No. 723,608, filed May 2, 1934.

This invention relates to processes wherein saturated hydrocarbons areconverted into olefins by catalytic dehydrogenation at elevatedtemperatures, the nature of the catalyst and the conditions of theconversion being such as to efiect simple dehydrogenation of thesaturated into the corresponding unsaturated hydrocarbon with veryslight decomposition of I the usual kind wherein the carbon chain breaksand smaller molecules are formed.

Catalytic d :hydrogenation is widely applied to organic compounds, moreparticularly to alcohols and hydrocarbons. The dehydrogenation ofalcohols is readily efl'ected at low temperatures in the presence ofvarious catalytic metals and metallic oxides. That class of hydrocarbonscontaining the hexamethylene ring may be dehydrogenated in a.characteristic manner into the corresponding aromatic hydrocarbons by asmall group of catalysts comprising the most active of the hydrogenationcatalysts. Both alcohols and hexamethylene hydrocarbons can besuccessfully dehydrogenated to yield molecular hydrogen and thecorresponding dehydrogenation :product at moderate temperatures, whichneed not exceed 300 C. The paraffin hydrocarbons, on the other hand,cannot be dehydrogenated at such low temperatures because of theunfavorable thermodynamic relationships. Temperatures in the range 450to 600 C. are required to obtain high extents of conversion and whiletemperatures somewhat below 400 C. will give a, measurable dissociation,a prohibitively low pressure or other artifice must be resorted to ifextensive conversion, exceeding ten per cent or so is to be effected. Inthis higher temperature range ordinary decomposition or cracking willtake place in the absence of a catalyst to yield smaller molecules byfracture of the carbon chain, and furthermore a protracted exposure tosuch temperatures will lead to the formation of tar and carbon whichwill deposit on any catalytic surfaces present and For these reasons anefiective dehydrogenation catalyst for paraflins specifically must meetcertain requirements not called for in the other cases. The activitymust be high to allow the dehydrogenation to be accomplished in a timeso short that cracking is not marked; the active nature of the surfacemust not be destroyed by the high temperatures; the composition andmechanical structure of the catalyst 'shoulddiscourage tar and carbonformation. Nickel, platinum, and palladium comprise the efiectivecatalysts for dehydrogenating hexamethylene hydrocarbons but these fallunder the conditions required for paraflins. Many other substances havebeen suggested for the dehydrogenation of paraflins which fail in one ormore respects. Many difllcultly reducible oxides, such as zinc oxide,magnesia, chromic oxide and others prepared in ordinary ways, show highdehydrogenating activity when applied to alcohols, but exhibit little orno dehydrogenating activity when applied to paraflins. The ultimatemechanism of the reaction is probably quite different from that of thealcohol dehydrogenation. The objectives to be achieved by the use ofmixtures as catalysts are far from parallel 'for the two fields ofcatalysts and the most eifective compositions for the two.purposes arewidely different. I

In U. S. Patent 1,905,383, there has been described the use of chromiumoxide in the form of a harddark colored vitreous gel for the purpose ofdehydrogenating paraflins. This catalyst is highly active in the usefultemperature range. The activity falls ofi during use and can be restoredby heating to 400-550" C. in an omgen containing gas which efiectsoxidation of deposited tar and carbon. At 550 C. to 600 C. however itpasses over into the common inert form of chromic oxide; the activity islost and cannot be restored by the oxygen treatment. At somewhat lowertemperatures the transformation requires one or more days but ultimatelytakes place within the elevated temperature range useful in practice forobtaining high conversions.

We have discovered that the addition of certain difiicultly reducibleoxides having little dehydrogenation activity in themselves will delayor prevent the transformation of chromium oxide into the inactive format temperatures within the working range. Most effective We have foundto be the infusihle oxides, alumina, zirconia, thorium oxide, silicondioxide, boric oxide, magnesium oxide and titanium dioxideincorporatedin the chromium oxide in such a way that the gelcharacteristics are conserved. This may be accomplished by precipitatingtogether from aque ous solution the gelatinous hydrous oxides ofchromium and one or more of the elements named. The two or more metallicsalts may be dissolved together in water and the hydrous oxidesprecipitated by an excess of alkali, preferably ammonium, sodium orpotassium hydroxide. The addition of a small amount of acetic acid priorto precipitation assists in maintaining the gel structure during thesubsequent drying of the REISSIUED OCT 28 1941 precipitate. Titaniumdioxide, boric oxide and silicon dioxide are of an acidic nature and arebest introduced in the form of their alkali salts in aqeous solution.Such. a solution may be introduced into the alkali solution used for theprecipitation before the. solution of the chromium or other salts isintroduced, or alternatively the two salt solutions may be poured at thesame time into the alkali-solution with vigorous stirring.

In some cases, particularly when silica is to be incorporated in amixture with chromium oxide, the hydrous oxides may best be precipitatedseparately and the gelatinous precipitates mixed before drying. Five percent or more of the diflicultly reducible oxide incorporated in chromiumoxide is usually required to eifect stabilization to heat. Higherproportions impart greater stability but a proportion so great as toreduce the chromium oxide content to below five per cent is usuallyundesirable since the activity is unduly decreased. The gelatinousprecipitate obtained by this procedure is washed with water, driedslowly in air, granulated, and finally heated to reaction temperature.Prepared in this way, the catalyst is obtained in hard glass granules.It is preferable to perform the heating prior to use in a stream ofhydrogen whereupon some reduction of the chromium oxides is effectedwith formation of water.

The catalyst prepared in this way may be supported in a suitablecontainer and the paraffin to be dehydrogenated passed over the catalystwhile a suitable reaction temperature of preferably 450-550" C. ismaintained.

The chromium oxide gel thus stabilized by theaddition of a difilcultlyreducible oxide will lose I activity during use, but the activity can berestored repeatedly by passing over the catalyst for a short time anoxygen containing gas while maintaining a temperature of 400-550 C.During the decay in activity, tar and carbon form in the catalystgranules and it is probably to this that the loss in activity must beattributed. We have found that the addition of small amounts of certainheavy metal oxides incorporated in the catalyst will bring about adecrease in the :rate at which activity is lost and the rate at whichcarbon forms. Thallium and bismuth oxides are most effective, lead andmercury oxides less so.

the metallic form in the catalyst during use.

The heavy metal oxides are incorporated in the catalyst mostconveniently by adding a soluble salt of the metal, preferably thenitrate to the chromium salt prior to dissolving and precipitating thehydrous oxides as described. Large proportions of the heavy metal oxidescannot be introduced without loss of the coherent gel structure. Usuallyless than mol. per cent should be incorporated in the catalyst and anaddition of 0.5 to 5 per cent will produce a great lessening in decay ofactivity during continued dehydrogenation.

The improved catalysts are effective for converting not only parailinsbut also alicyclic or aromatic hydrocarbons containing alkyl substituentgroups of two or more carbon atoms into the corresponding unsaturatedhydrocarbons of the same number of carbon atoms per molecule but oflower hydrogen content. Oleflns containing at least four carbon atomsper molecule can similarly be converted into dioleflns. Temperatures inthe range 300 to 600 C. give best results. The reaction rate with thecatalysts described in high and equilibrium extent of dissociation isreadily attained. We have found that the lower temperature at whichequilibrium dissociation is small may be at the lower pressures. whichfavor dissociations," or whenftreating'gthe' -higher molecular weighthydrocarbons, for which the thermodynamic equilibrium dissociation islarge at the lower temperatures. The dissociation is repressed by. 1 18bpressures, and pressures exceeding a few atmospheres are accordinglyundesirable. Pressures in the neighborhood of atmospheric give goodresults, and pressures below atmospheric permit still greaterdissociation.

Where thecatalysts are used to eifect hydrogenation of oleilns ordioleflns, temperatures of 200 to 500" C.;may"be used, preferably thelower temperatures and a high partial pressure of hydrogen and pressuresabove atmospheric are desirable butnot necessary. These catalysts ex-80111118 "bv sul 'amm m a.

Example 1.--An aqueous renames nitrate and'aluminum nitratecontainingthe salts in the molar ratios of-oneto onefwasiintrodueed intoanexcess 'of' dilute 11' The.

gelatinous precipitate of hy angea;

ides was then washed with water thoroughly,- 111;

tered off, dried slowly in air to a; glassy g'eland.

granulated. A 5 cc. portion of thegranularfgel was supported in acatalyst tube'and aistreani of n-butane passed over it at rate of litersper hour while the temperaturewas at 450 C. A 12 per cent conversioninto butenes plus hydrogen was obtained. 'I'he'activity de-' cayedduring use; thefconversion fell .to-G per cent during 14 hours. The nowof butane interrupted, the catalysttreate'd with oxygen at 450 C. andthe catalyst wasji'ound tohave been restored ;-to original activity. Thecatalyst was used and restoredto original activity in this way manytimes. A chromium oxide gelcontaining no added metals or other oxideswhich wasused and reactivated in the same way'suffered a serious loss inactivity after .two reactiv'atiohs by oxygen.

Example 2. A chromium oxideealuminumloxide gel was prepared as inlilxamplel except that 2 mol. per cent of thallium nitrate wasincorporated in the solution of the other metallic salts.

The conversion of butane, carried out in thesame 1. In a process forhydrogenating unsaturated hydrocarbons, the steps which comprisepassingthe said unsaturated hydrocarbons together with way, proceeded for 72hours before extent of conversion fell to 6 per cent'and the catalystwas' hydrogen at temperatures above 200C, in con-' 7 tact with avitreous gel catalyst comprising chromium oxide and a dimcultlyreducible oxide of the group aluminum, zirconium, titanium, silicon,thorium, boron, and magnesium, thef'said oxides having been combined inav state of intimate association effected whilethe oxides are in ahighly hydrous condition.

2. In a process for hydrogenatingunsaturatedj .hydrocarbons, the stepswhich comprise the said unsaturated hydrocarbons together with hydrogenat temperatures above 200 C.'in con tact with a vitreous gel catalystcomprisingchroe mium oxide and a diilicultly reducible oxide ofthe groupaluminum, zirconium, titanium, silicon, thorium, boron, and magnesium,the said oxides having been combined in astate of intimate associationeffected while the oxides are in a highly hydrous condition, and also atleast .5 mol. percent 01' a readily reducible oxide of the group,thallium oxide, mercury oxide, bismuth oxide and lead oxide. 7

3. In a process ior hydrogenating unsaturated hydrocarbons, the stepswhich comprise passing the said unsaturated hydrocarbons together withhydrogen at temperatures above 200 C. in contact with a vitreous gelcatalyst comprising chromium oxide and a dimcultly reducible oxide ofthe group aluminum, zirconium, titanium, sllicon, thorium, boron, andmagnesium, the said oxides having been combined in a state of intimateassociation eflected while the oxides are in a highly hydrous condition,continuing said passage until the activity of said catalyst becomesreduced, and then restoring the activity of said catalyst by subjectingit to treatment with an oxygen containing gas at an elevatedtemperature.

FREDERICK E. FREY. WALTER F. HUPPKE.

